The effectiveness of biofeedback has been a subject of controversy because biofeedback
a. has no reported side effects
b. cannot be effectively tested
c. has no reported negative effects
d. requires uncomfortable electrodes

The effectiveness of biofeedback has been a subject of controversy because biofeedback "cannot be effectively tested".

Biofeedback is a kind of treatment that utilizes sensors joined to your body to gauge key body capacities. Biofeedback is proposed to enable you to take in more about how your body functions. This data may assist you with developing better authority over certain body capacities and address health concerns.  

Biofeedback is based on the idea of "mind over issue." The thought is that, with appropriate methods, you can change your health by being aware of how your body reacts to stressors and other upgrades.

to provide benchmarks